Held: Friday, 13 February 2015

Back to Outline 14 - Transforming Colors. On to Outline 16 - Transforming Images.

Summary

We consider the ways in which Scheme supports yes/no questions and procedures that can be used to ask such questions. We also see how such procedures can provide another form of control.

Related Pages

• Reading: Boolean Values and Predicate Procedures
• Lab: Boolean Values and Predicate Procedures
• EBoard (Source) (HTML)

Overview

• Boolean values.
• Predicates - Procedures that return Boolean values.
• Combining booleans with and and or.

Administrivia

• Continue partners!
• Mentor session Monday at 7:00 p.m.
• Just in case it's not clear: If I find that you have posted your exam work online, including via social media, I will report you for ethical violations and, unless prevented by College policy, will fail you in the class.
• Friday the 13th falls on Friday this month. Be careful.
• Weekly PSA.

Upcoming Work

• Homework.
  • Due Tuesday night at 10:30 p.m.
• No lab writeup for today
• Reading for Monday:
  • Transforming Images

Extra Credit Opportunities

Academic

• TEDx Grinnell, February 21
• Pioneer Diversity Council talk

Peer Support (Morning Section)

• Swimming, Conference Championships, February 13-15, The Osgood
• Indoor track and field, Saturday.
• Julia's radio show, "The Hot Box". Wednesday night/Thursday morning 1:00-2:00 a.m.

Peer Support (Afternoon Section)

• Swimming, Conference Championships, February 13-15, The Osgood
• Indoor track and field, Saturday.
• Men's Basketball vs. Knox, next Wednesday at 7:30 p.m., New Darby

Recommended, But no EC

• 2 <3 GC day next Wednesday.

Preparation

• What did you learn from the reading? (Let's try to summarize for each other.)
• What questions do you have?

or and and as control structures

• How does normal procedure application work?
  • Evaluate all the parameters
  • "Plug them in to the body"
  • Evaluate the body
• How does or work?
  • It evaluates each parameter, in turn, until one holds (or it runs out of parameters).
  • As soon as one holds, it stops and returns that value.
• How does and work?
  • It evaluates each parameter, in turn, until one fails to hold (or it runs out of parameters).
  • As soon as one fails to hold, it stops and returns #f.
• This evaluation strategy means that we can use and and or to evaluate a sequence of expressions, stopping when we get the first acceptable one.

Lab

• Work on the lab
• Be prepared to discuss!